ENGINE KEEPS CUTTING OUT

[RichardMorgan]

Hi, I know I'm not a member, but could you please help me out?
On a long journey when the car has been running for a while, the engine keeps cutting out and will not tick over in traffic or at lights. Have you any ideas how I could sort this out?
Really hoping you'll help us, thanks, Phill.
[email protected] Posted by Richard Morgan

[crazylegs]

do a fault code check and see what comes out.my first thought would be a temp sensor.get back to us with the code.

[kaiowas]

One of mine does this too but the engine is in generally poor health (low compression, burns oil)

Any idea if this car has similar symptoms or is this problem not related?

[System-G]

I had this problem with mine on both the original '85 engine and the replacement '88 engine.

Apparently, it quite common, I think Chris (aka Limeymk1) also had similar problems.

It's more than likely going to be the TPS (Throttle Possition Sensor) on the throttle body controling the "butterfly". They can often start giving incorrect values. I metered the terminals on mine and found the values were marginally out. They can be adjusted by using a multi-meter, a feeler gauge and by turning the TPS clockwise or anti-clockwise. It's fully explained in both the Haines Manual and the BGB.





Now after adjusting mine, I find the car doesn't cut out after long runs. But it sometimes does have difficulty restarting after a long run after being switched off for a short time. I must have got the values ever so slightly wrong, but it doesn't worry me as I don't do many short stops after long runs.

[JMR_AW11]

When you stop the engine after a long run the coolant temperature in the head by the THW coolant sensor will rise by at least 7 degrees. The heat from the centre of the head soaks through and lifts the coolant temperature. This takes it above the normal max running temperature. When the car is restarted the ECU thinks the engine is very hot and this affects the fuelling and ignition timing.

The ECU has 'over temperature' maps in it and these could be causing the poor starting.

It might be worth looking at the health of the cooling system for your cars.
If the radiator is sludged up, maybe the coolant temperature will be higher than normal and you could be creeping into the over temperature maps in the ECU and causing the stalling symptoms in the original post. The more sludge, the further you may creep into the over temp maps on a long run. Try flushing and refilling the coolant system.

The flushing requires prior knowledge of the MR2 coolant system and the MR2 mk1 club website should have links to help you with this. Keeping the coolant system healthy is one of the best things you can do for your MR2.

[spudgun]

It wouldn't be the old leaky fast idle valve again would it?

With the recent warm weather you might find that it is actually closing properly now. If someone has tried to set the idle with this valve leaking it will onlt be drawing a small portion of air through the idle curcuit, so it will stall once the cold idle valve shuts properly. just a thought.

[System-G]

When you stop the engine after a long run the coolant temperature in the head by the THW coolant sensor will rise by at least 7 degrees. The heat from the centre of the head soaks through and lifts the coolant temperature. This takes it above the normal max running temperature. When the car is restarted the ECU thinks the engine is very hot and this affects the fuelling and ignition timing.

The ECU has 'over temperature' maps in it and these could be causing the poor starting.

It might be worth looking at the health of the cooling system for your cars.
If the radiator is sludged up, maybe the coolant temperature will be higher than normal and you could be creeping into the over temperature maps in the ECU and causing the stalling symptoms in the original post. The more sludge, the further you may creep into the over temp maps on a long run. Try flushing and refilling the coolant system.

The flushing requires prior knowledge of the MR2 coolant system and the MR2 mk1 club website should have links to help you with this. Keeping the coolant system healthy is one of the best things you can do for your MR2.

In my case with the poor starting after a long run, I haven't noticed the temp gauge rise at all. But then again I suppose the gauge itself drops to zero when the engine is off
A couple of months before doing my engine swap, I did a complete flush, re-fill and bleed of my coolant system. And again when we did the engine swap, a full flush, re-fill and bleed was done. Infact the cooling system was the bain (sp?) of the engine swap as the donor engine needed new water pump and coolant pipes, but we only discovered this once the engine was fitted and we were filling with coolant.

Whilst the engine was cutting out after long runs, I never had the problem of poor starting after switching off after a long run. The poor starting after long runs only started to happen ocasionally after we adjusted the TPS.

[JMR_AW11]

In my case with the poor starting after a long run, I haven't noticed the temp gauge rise at all. But then again I suppose the gauge itself drops to zero when the engine is off

Although I've never traced the wiring to prove it I believe the ECU uses its own unique sensor to measure the coolant temp. The dash guage uses a coolant sensor located elsewhere.

The ECU THW sensor DOES show a sharp rise after the engine stops because I have monitored it with a laptop. It falls back quite quickly once the car starts and the coolant recirculates.

BTW, the UK MR2 ECU doesn't pay much attention to the exact voltage read back from the TPS wiper. Being a speed density EFI system knowing the exact throttle position is not necessary for correct fuelling and ignition. (In fact you don't need to know the throttle position at all) The EFI and ignition timing is determined from the RPM and the MAP sensor readings. The TPS voltage has only a crude (two settings!) effect on the mk1 MR2 fuelling.

The TPS also contains a microswitch called IDL which may give strange symptoms if it is faulty or misaligned. This switch lets the ECU know the driver has his/her foot off the throttle and the ECU then runs the idle routines. I would guess this is what you had the most success with tweaking/fixing.